The Collaborative International Dictionary of English v.0.48:

Recrudescence \Re`cru*des"cence\ (r?`kr?*d?s"sens),
Recrudescency \Re`cru*des`cen*cy\ (-d?s"sen*s?), n. [Cf. F.
   recrudescence.]
   [1913 Webster]
   1. The state or condition of being recrudescent.
      [1913 Webster]

            A recrudescence of barbarism may condemn it [land]
            to chronic poverty and waste.         --Duke of
                                                  Argyll.
      [1913 Webster]

   2. (Med.) Increased severity of a disease after temporary
      remission. --Dunglison.
      [1913 Webster]

WordNet (r) 3.0 (2006):

recrudescence
    n 1: a return of something after a period of abatement; "a
         recrudescence of racism"; "a recrudescence of the symptoms"

Moby Thesaurus II by Grady Ward, 1.0:

47 Moby Thesaurus words for "recrudescence":
   amendment, atavism, backset, backward deviation,
   change of allegiance, change of heart, change of mind,
   falling back, improvement, lapse, new birth, palingenesis,
   palingenesy, reanimation, rebirth, reclamation, recurrence,
   redemption, reform, reformation, refreshment, regeneracy,
   regenerateness, regeneration, regenesis, regression, rejuvenation,
   rejuvenescence, relapse, renaissance, renascence, renewal,
   resurgence, resurrection, resuscitation, return, reversal, reverse,
   reversion, revival, revivescence, revivescency, revivification,
   second wind, second youth, setback, throwback